I have the ultralight. My dimensions: 40" chest. 31" waist. I can buy almost any medium off the rack and it fits. My dress jacket size is 40 with no alteration. I am right at the upper end of the medium size for Patagonia and Montbell.
The ultra light fits like my tailored made suits from Hong Kong. It is a layer piece, but I can make it by with a light sweater underneath, but the armpits are a bit tight.
Material is light ripstop. There is no drawcord at the waist. The pockets are now zipped, but mine is the older version.
I put it under a hard shell, or a hoodless softshell and I am warm into the upper 20's.
It packs small. I took it to Glacier last year and wore it in the evening with a t shirt underneath. Worked great.
The material is light. It is shiny. The jacket is NOT PUFFY. It will not make you look goofy or fat uptop. You can beat this up quick if you are rubbing up against things and it will rip if you are around sharp objects.
Tight at the waist. THIS IS SLIM FIT, probably the slimmest fitting synthetic jacket our there. Unless you are of athletic build SIZE UP.